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Introduction

Field Map Constrained Nonrigid Registration Method for Correction of Distortions in Echo Planar Images. Yong Li 1 , Ning Xu 1 , J. Michael Fitzpatrick 1,2 , Victoria L. Morgan 2 , David R. Pickens 2 , Benoit M. Dawant 1,2

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Introduction

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  1. Field Map Constrained Nonrigid Registration Method for Correction of Distortions in Echo Planar Images Yong Li1, Ning Xu1, J. Michael Fitzpatrick1,2, Victoria L. Morgan2, David R. Pickens2, Benoit M. Dawant1,2 1Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN, USA 2Vanderbilt University Institute for Imaging Science,Department of Radiology and Radiological Sciences, Vanderbilt University , Nashville, TN, USA

  2. Introduction • Two common retrospective distortion correction methods for Echo Planar (EP) images • Field map based [1,2] • Field map measurement • Regularization & unwrapping • Nonrigid registration based [3-5] • Constraints &Optimization [1] P. Jezzard,et al.,MRM,34:65-73,1995 [2] R. Cusack, et al., NeuroImage,127-142, 2003 [3] C. Studholme, et al., TMI, 1115-1127, 2000 [4] J. Kybic, et al., TMI, 80-93 2000 [5] Y. Li, et al., Med Im 2006: Im Proc, in press

  3. Methods Unidirectional Deformation Jacobian factor Rephasing factor (for GE images) Physical Constraints Initial Deformation Field Final Deformation Field Nonrigid Registration Corrected EPI Field map Spatial Adaptation of Transformation Properties EP Image

  4. Results Fig. 1 a. distortion free EP image; b. distorted image; c. difference between a and b; d, e: differences between distortion-free EP image and corrected images with field map method (d) and our approach (e); f: histogram of difference images.

  5. Results Fig. 2 a: reference image b: distorted image overlaid on reference image c, d: images corrected with SPM FieldMap toolbox [6] (c) and our approach (d) overlaid on reference image (b, c and d are magnified to show the differences) [6] http://www.fil.ion.ucl.ac.uk/spm/toolbox/fieldmap/

  6. Conclusions • Combination of field map and nonrigid registration methods for distortion correction in EP images is proposed. • Field map is used both to initialize and to constrain the nonrigid registration algorithm, which improves on results obtained with either method alone. • Ongoing work includes evaluating this approach on real fMRI data. Acknowledgements NIH grant R01-NS46077 http://vuiis.vanderbilt.edu/fmriphantoms/

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